Amount for accounts payable to related parties.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

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Reflects the sum of all other revenue and income realized from sales and other transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party during the period.

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Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

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Related Party Transactions (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017	Oct. 31, 2014
Related Party Transaction [Line Items]
Accounts Payable, Related Parties	$ 83
Line of Credit [Member] \| Brightstar [Member]
Related Party Transaction [Line Items]
Line of credit facility, maximum borrowing capacity				$ 700
Brightstar [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	65	$ 93	$ 64
Related Party Transaction, Other Revenues from Transactions with Related Party	194	154
Revenue from Related Parties	$ 1,890	$ 1,922	$ 1,682